Embryonic and somatic stem cells have the ability to differentiate into any cell type; they are therefore uniquely suited for cell replacement therapies for diseases which ravish, or damage/injury to, a defined cell population. Beyond their direct therapeutic value, lineage specific differentiated stem cells are also valuable research tools for a variety of purposes including in vitro screening assays to identify, confirm, test for specification or delivery of therapeutic molecules to treat lineage specific disease, further elucidation of the complex mechanisms of cell lineage specification and differentiation, and identifying critical biochemical differences between normal and diseased or damaged states which can be further contemplated for use as diagnostic or prognostic markers.
The power of embryonic and somatic stem cells as therapeutics and model systems for neurodegenerative diseases has been well explored. However, much of the research and technological developments relating to directed differentiation of embryonic and somatic stem cells has taken place in the field of diseases of the central nervous system (CNS), such as Huntington's, Alzheimer's, Parkinson's, and multiple sclerosis. There is a current lack of knowledge relating to the directed differentiation of embryonic and somatic stem cells toward lineages of the peripheral nervous system (PNS). The PNS is comprised of the somatic nervous system, which coordinates muscular-skeletal control and sensation of external stimuli, and the autonomic nervous system, which regulates inner organ function such as heartbeat and respiration. There are multiple diseases of the PNS including Charcot-Marie-Tooth disease, Gillian Bane Syndrome, and Hirschsprung's disease. Diseases of peripheral sensory neurons of the PNS are of particular societal burden because they result in severe pain or failure to respond to noxious stimuli causing injury and include diseases such as Familial Dysautonomia, congenital insensitivity to pain, diabetic neuropathies, and damage due to infections of Varicella or herpes zoster.
Understanding the pathology of peripheral sensory neuron diseases, as well as development of treatment modalities, is hindered by the difficulties in obtaining human peripheral sensory neurons; current methods are limited to manual isolation from 3-5 week old human embryos or rare surgical procedures. The directed differentiation of embryonic stem cells or somatic stem cells into specified peripheral sensory neurons, in particular nociceptors which are the pain sensing peripheral sensory neurons, would be an ideal reproducible source of such cells for both research and therapeutic application. Recent attempts to produce peripheral sensory neurons from neuronal intermediates derived from embryonic stem cells have been made. However, these techniques are limited by the need for a neuronal intermediate, co-culture with murine stromal cells, length of time to derive such peripheral sensory neurons, low yield, impure populations of cells containing mixed neuronal types, limited survival and poor characterization of PNS generated neurons.
Therefore there is a need in the art for a method to produce peripheral sensory neurons, in particular nociceptors, directly from embryonic or somatic stem cells without the use of contaminating murine stromal cells with increased purity and yield.